含时黄金规则波包传播法对低初始振动激发HeI_2分子振动预离解的研究

A Time-Dependent Golden Rule Wave Packet Treatment for Vibrational Predissociation of HeI_2 Molecule for Low Initial Vibrational Excitations

采用含时黄金规则波包传播法，对低振动激发（ν＜１２）ｖａｎｄｅｒＷａａｌｓ分子ＨｅＩ２（总角动量Ｊ＝０）的振动预离解计算了总和部分衰变宽度。几乎对所有初始振动态，得到的总衰变宽度比线宽测量外推数据低约３０％。但是在很低振动激发（ν≤２）时。计算结果相当接近于实验外推数据。所得到的总衰变宽度随初始振动态的变化呈现一种非线性关系，这与较高振动激发的情况很相似。因此，低振动激发时总衰变宽度的变化不可能是源于离解机理改变的结果。衰变模式仍应是量子力学的。像在高振动激发时得到的结果一样，计算的转动态分布对初始振动还是不敏感的。

We have presented a calculation for the total and partial decay widths for vibrational predissociation for a low vibrational excited van der Waals molecule HeI_2. The time-dependent golden rule wave packet method has been used in our numerical calculation for the decay widths. Nearly all of the computed decay widths are consistently underestimated by about 30% than those extrapolated from linewidth measurements. But,it is interested to note that computed decay widths for very low initial vibrational excitation (v≤2) are quite close to that deduced from the measured vibrational predissociation rates. Our obtained decay widths as a function of initial vibrational quantum numbers ν display a highly nonlinear behavior, similar to that for higher initial vibrational excitation. It naturally means that a quantum mechanical decay mode remains as well for low vibrational excitation, in which the variation in decay widths may not the an effect due to a change in the dissociation mechanisms. The rotational state distributions from our calculation are still insensitive to the initial vibrational states, which has also been observed in the case of higher vibrational excitation.